During sex, the male penetrates the female, but shifts his body opposite to hers and, while on all fours with his legs spread in a fashion analogous to a frog, proceeds to bare butt fart directly in her face, thusly mimicking the deep and guttural "ribbit" of a bullfrog. Note that bare butt farting has been referred to as "the future of sex" in some forward thinking academic circles.

When someone puts their mouth directly over another person's butt-hole prior to a fart. The person then catches the fart in their mouth by inhaling the fart into said mouth. The end result is a person that looks like a bullfrog.

A: I'm about to fart.
B: I'm all about bullfrogging you...lay face down.